I prefer Dells mainly because my three year old Dell laptop is still going strong with no major hardware issues besides someone frying the hard drive. Then again, wasn't a big deal since it was only a 250GB, and I wanted a bigger one anyway at the time.
Alienware, find the right discounts. They are built very well and are fast. As long as you spend alot. My current rig ran me 3000$ before discounts 1700$ out the door. m17x r3 6990m, i7 2820 2 250gb ssds in raid 0 8gb ram.